Good question and a good idea…
Take a look at the example below. You can set up a journal in whatever format will be easiest for you to use and understand. The data points that are shown below are the primary headings that should be included.
In the Notes/Remarks section, you can include what prompted you to enter the trade, what indicators were used, market conditions at the time, any relevant news announcements and similarinformation that would be helpful. Also, when the trade is closed, include a few words as to why you feel the trade was profitable or not. The overriding point here is that when you go back to look over the trade, you would like to be able to reconstruct it as accurately as possible and use that information going forward.
The benefit of keeping a journal is that over days, weeks and months you can go back and see what you might be doing that is leading to successful trades and, likewise, what might be leading to unsuccessful trades.
Also, the mere fact of having to write down key data on each trade will cause you to think through each trade in a little more depth right from the start.
Lastly, for some added thoughts on this subject, the link below will take you to one of the Daily Trading Lessons by Tom Long on Keeping a Trading Log...